Narrated Abdullah bin Buraidah from Yahya bin Ya'mur who said:
The first person to speak about Al-Qadar was Ma'bad Al-Juhani. He said: Humaid bin Abdur-Rahman Al-Himyari and I went out until we reached Al-Madinah, and we said: 'If we could only meet someone among the companions of the Prophet (ﷺ) so we could ask him about what those people have innovated. [He said:] So we met him - meaning Abdullah bin 'Umar - while he was leaving the Masjid. [He said:] My companion and I were on either side of him. [He said:] I thought my companion was going to leave the speaking to me so I said: O Abu Abdur-Rahman! There is a group of people who recite the Qur'an and seek knowledge, and they claim there is no Al-Qadar, and that the affair is left to chance.' He said: Whenever you meet those people, then tell them that I am not of them and they are not of me. By the One Whom Abdullah swears by! If one of them were to spend gold the like of Uhud (mountain) in charity, it would not be accepted from him until he believes in Al-Qadar; the good of it and the bad of it.' He said: Then he began to narrate, he said: 'Umar bin Al-Khattab said: We were with the Messenger of Allah when a man came with extremely white garments, and extremely black hair. He had no appearance of traveling visible on him, yet none of us recognized him. He came until he reached the Prophet (ﷺ). He put his knees up against his knees, and then said: O Muhammad! What is Iman?' He said 'To believe in Allah, His Angels, His, Books, His Messengers, the Day of Judgement, and Al-Qadar, the good of it and the bad of it.' He said: 'Then what is Islam?' He said: 'Testifying to La Ilaha Illallah, and that Muhammad is His servant and Messenger, establishing the Salat, giving the Zakat, performing Hajj to the House, and fasting (the month of) Ramadan.' He said: 'Then what is Ihsan?' He said 'That (is) you worship Allah as if you see Him, and although you do not see Him, He certainly sees you.' He said: 'For all of those he replied to him: 'You have told the truth.' He said: So we were amazed at him, he would ask, and then tell him that he is telling the truth. He said: 'Then when is the Hour?' He (ﷺ) said: 'The one being asked knows no more than the questioner.' He said: 'Then what are its signs?' He said: 'That the slave woman gives birth to her master, and that the naked, poor, and bare-footed shepherds rival each other in the height of the buildings.' 'Umar said: 'Then the Prophet (ﷺ) met me three days after that and said: 'O 'Umar! Do you know who the questioner was? It was Jibril. He came to teach you about the matters of your religion.'